The present invention relates to a device and method for separating a luminance signal (Y) and/or a chrominance signal (C) from a composite video signal.
In recent years, as TV receivers have been increasingly upsized and enhanced in image quality, higher importance has been placed on enhancement in the performance of a Y/C separation device for separating a luminance signal (Y) and a chrominance signal (C) from a composite video signal.
A conventional Y/C separation device will be described with reference to FIG. 11. FIG. 11 is a block diagram of a Y/C separation device disclosed in Japanese Laid-Open Patent Publication No. 5-111051. Referring to FIG. 11, an input terminal 31 receives a band-limited chrominance signal output from a multi-line comb filter. Delay circuits 32 to 35, connected to the input terminal 31 in series, respectively delay the input signal by a half period of the chrominance signal and output the delayed signal. Inverter circuits 36 and 37 are connected to the delay circuits 32 and 34, respectively. Minimum circuits 38 to 45 are placed to receive the delayed signals. The minimum circuits 38 to 42, respectively having three input terminals, select the minimum signal among signals input at the three input terminals and output the selected signal. The minimum circuits 43 to 45, respectively having two input terminals, select the minimum signal among signals input at the two input terminals and output the selected signal. Specifically, the three input terminals of the minimum circuit 38 receive the signals from the inverter circuit 37, the delay circuit 35 and the input terminal 31. The three input terminals of the minimum circuit 39 receive the signals from the delay circuit 35, the input terminal 31 and the inverter circuit 36. The three input terminals of the minimum circuit 40 receive the signals from the input terminal 31, the inverter circuit 36 and the delay circuit 33. The three input terminals of the minimum circuit 41 receive the signals from the inverter circuits 36 and 37 and the delay circuit 33. The three input terminals of the minimum circuit 42 receive the signals from the delay circuits 33 and 35 and the inverter circuit 37. The two input terminals of the minimum circuit 43 receive the signals from the inverter circuit 37 and the delay circuit 33. The two input terminals of the minimum circuit 44 receive the signals from the inverter circuit 36 and the delay circuit 33. The two input terminals of the minimum circuit 45 receive the signals from the inverter circuits 36 and 37. The output signals of the minimum circuits 38 to 42 are supplied to a maximum circuit 46, which selects the signal having the maximum amplitude among the five input signals and outputs the selected signal as a chrominance signal via an output terminal 47. The output signals of the minimum circuits 43 to 45 are supplied to a maximum circuit 49, which selects the signal having the maximum amplitude among the three input signals and outputs the selected signal to a subtractor 50. The subtractor 50 subtracts the output signal of the maximum circuit 49 from a composite video signal input at an input terminal 51 and outputs the result as a luminance signal via an output terminal 52.
The operation of the Y/C separation device configured as described above will be described.
FIG. 8 shows output waveforms on the side of the maximum circuit 49 obtained when a 1-period chrominance signal is input at the input terminal 31. FIG. 10 shows output waveforms on the side of the maximum circuit 46 obtained when a 1.5-period chrominance signal is input at the input terminal 31. Description on the progress of the operation of this device is omitted here. See Japanese Laid-Open Patent Publication No. 5-111051 for details. The same reference codes as those used in this publication are used herein for easy reference. On the side of the maximum circuit 49 in FIG. 11, any input signal of one period or more is recognized as a chrominance signal. Therefore, an input 1-period signal is output as it is from the maximum circuit 49. On the side of the maximum circuit 46 in FIG. 11, any input signal of 1.5 periods or more is recognized as a chrominance signal. Therefore, an input 1.5-period signal is output as it is from the maximum circuit 46.
The conventional Y/C separation device described above recognizes input of a signal of 1.5 periods or more as input of a chrominance signal. Therefore, while the device can remove a signal representing input of a fine oblique line of one period or less, for example, it fails to remove a signal representing continuous input of an oblique line, for example, and thus is poor in cross-color suppression effect.